Omission of Radiation in Elderly Patients in a Predominantly Minority Population

Abstract

<h3>Purpose/Objective(s)</h3> The omission of radiation (RT) has increased among elderly patients following the results of CALGB C9343 and more recently PRIME II demonstrating low local recurrence (LR) risk with adjuvant endocrine therapy (ET) alone for women over 70 with estrogen receptor positive (ER+) Stage I breast cancer. However, these trials were conducted in predominantly Caucasian populations and may not be generalizable to more diverse populations. The aim of this study was to evaluate the risk factors for LR without RT in ER+ Stage I disease among elderly women in a largely minority patient population. <h3>Materials/Methods</h3> This study is a retrospective analysis of elderly patients (≥70) with Stage I ER+ breast cancer who underwent lumpectomy and were considered for RT at an urban, academic institution between 2006 to 2020. The primary endpoint was mammographic LR at 5 years, stratified by use of adjuvant RT. Demographic and clinical variables, including pathology (grade, LVI, Her2 status), compliance with ET (defined as at least 1 year), imaging, and follow-up information were obtained from the electronic medical record. Fisher's exact test was used for categorical variables. <h3>Results</h3> Three hundred and sixty-nine patients were included in the initial analysis with a median follow-up time of 6.2 years. Median age was 75.8 years (interquartile range [IQR] 72.4-79.5), with 78% identifying as either Hispanic or non-Hispanic black. 33% of patients omitted adjuvant RT, and 89% were compliant with adjuvant ET. There was a total of 18 LRs at a median of 4.1 years (IQR: 2.3 – 5.5 years). Of these, 13 omitted RT, 2 were LVI+, 3 were grade 3, 2 were Her2+, 11 were non-compliant with ET, and 0 identified as non-Hispanic Caucasian. 11 patients who had a LR omitted both RT and ET. Amongst those with follow-up of at least 5 years (225 patients), there were 11 LRs. The use of RT led to a significant reduction in 5-year LR (1.4% vs 14%, p <0.001). There was a trend toward increased LR in minority patients (6.7% vs 0%, p=0.125) regardless of receipt of RT. <h3>Conclusion</h3> In this retrospective analysis of elderly, mostly minority, stage I post-lumpectomy ER+ breast cancer patients, we observed a significant reduction of LR with the use of adjuvant RT in line with prior studies. However, omission of RT led to higher than anticipated LR likely due to adjuvant ET non-adherence. Whether ethnicity is a truly factor in LR would require larger confirmatory studies.